Radio detection apparatus



May 5,, 1970 MASARU WATANABE ETAL 3,51

RADIO DETECTION APPARATUS Filed July 10, 1968 2 Sheets-Sheet 1 FIG.

(PR/0R ART) ANTENNA #I.

7' 24. PHASE 7 7' 20 '7 SHIFTER 1 SUBTRACTION Q cmcun' 1 MATRIX 5 DATA mfi 22 PROCESSING SUBTRACTION Q cmcun TRANSMITTED T WAVEFORM RECEIVED WAVEFORM R2 y 1970 MASARU WATANABE ETA!- 3,510,371

RADIO DETECTION APPARATUS Filed July 10; 1968 2 Sheets-Sheet a FIG. 3

ANTENNA 1H 36 40 I6 0 f I f T R TIME PHASE E DELAY SHIFTER 20 34 [1 LINE? 4 1 I 58 is I J PHASE SUBTRACTION mien SHIFTER CIREUIT 2 MATRIX a 42 4 P DATA aocessms FILTER J'fiEY 22 oavncE f LINE? 7 j azzw 44 FILTER f Ill 1 TRANSMITTED u WAVE FORM RECEIVED 4 WAVEFORM l' l FIG. 4

RECEIVED WAVE FORM 4 U-S. Cl. 343-16 7 Claims ABSTRACT OF THE DISCLOSURE At least two antenna elements of the same radiation characteristics disposed in a common vertical plane are spaced away from each other by a distance greater than one .half an operating wavelength and one of them periodically transmits radio frequency pulses, each of which consisting of a plurality of continuous radio frequency pulses having different frequencies and a common duration. An echo received by all the antenna elements is divided into pulses having the different frequencies. These pulses are suitably time-delayed to cause them to coincide in time with one another and then shift in phase angle by predetermined different magnitudes. For each frequency a vectorial subtraction is effected with the pulses to form a multiple-lobed directional pattern. The patterns are combined in pairs together to cause a selected lobe in one of each pattern pair to coincide with a selected lobe in the other of that pair at a specified angle of elevation with the coinciding lobes different in angle of elevation from one to another combination of patterns. The mainlobes thus formed are arranged to cover partly or entirely a space to be searched.

BACKGROUND OF THE INVENTION This invention relates to a radio detection apparatus including antenna elements disposed at intervals greater than one half an operating wavelength in a common vertical plane.

The prior art type of radio detection apparatus has included either an antenna array including a plurality of antenna elements disposed at different intervals in a common vertical plane and operative with a predetermined common ferquency or an antenna array including a plurality of antenna elements disposed at predetermined intervals in a common vertical plane and operative with two or more different frequencies. The radio detection apparatus including the first-mentioned antenna array has been disadvantageous in that because of the necessity of providing a plurality of antenna element interval values, the number of antenna elements and therefore the overall scale of the antenna array is large. The apparatus including the last-mentioned antenna array has been advantageous for the purpose of decreasing the number of antenna elements but it has been disadvantageous in that two or more different frequencies should be simultaneously used resulting in an increase in scale of a transmitter device involved.

SUMMARY OF THE INVENTION t hitedi. States Patent O use of the greater part of a transmitter device involved leading to a decrease in scale of the latter.

The invention accomplishes the above cited objects by the provision of a radio detection apparatus comprising, in combination, an antenna array including at least two antenna elements of the substantially same radiation characteristics disposed in a common vertical plane to be spaced away from each other by a predetermined interval greater than one half an operating wavelength, one of the antenna elements serving to periodically transmit a radiofrequency signal while all the antenna elements are adapted to receive an echo and means for processing the echo to form a multiple-lobed directional pattern of the antenna array, characterized in that the radio-frequency signal consists of a plurality of continuous radio-frequency pulses having different frequencies and a common duration and successively arranged with respect to time to form no spacing therebetween and that there are provided filter means for dividing the received echo into radiofrequency pulses each of which having one frequency and common duration, means for processing the divided pulses of the same frequency to form a multiple-lobed directional pattern of the antenna array for each of the said different frequencies, and data processing means for combining the multiple-lobed directional patterns in pairs together.

Preferably, a selected lobe in one of each pair of the combined directional patterns may coincide with a selected lobe in the other of that pair at an angle of elevation such that the coinciding lobes are different in angle of elevation from one to another combination of the directional patterns to cover partly or entirely a space to be searched.

The apparatus may advantageously include time delay circuit means for imparting different time delays to the respective divided pulses to permit the pulses to be processed at a common time point, and operational circuit means for vectorially subtracting the divided pulses for each of the different frequencies to form the multiplelobed directional patterns.

BRIEF DESCRIPTION OF THE DRAWINGS The invention will become more readily apparent from the following detailed description taken in conjunction with the accompanying drawings in which:

FIG. 1 is a schematic diagram of a radio detection apparatus constructed in accordance with the teachings of the prior art;

FIG. 2 is waveforms of transmitted and received signals used in the apparatus shown in FIG. 1;

FIG. 3 is a schematic diagram of a radio detection apparatus constructed in accordance with the teachings of the invention; and

FIG. 4 is waveforms of transmitted and received signals suitable for use in the apparatus shown in FIG. 3.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring now to the drawings and FIG. 1 in partic ular it is seen that an arrangement disclosed herein com' prises three antenna elements Nos. 1, 2, and 3 disposed at predetermined different intervals a and d; and designated by the reference numerals 10, 12 and 14 respectively, a first phase shifter 16 electrically connected to second vectorial subtraction circuit 22 having the other input electrically connected to the antenna element 14.

For purpose of illustration, the combination of the antenna element 10 and an electrical conductor extending therefrom to the first phase shifter 16 may be hereinafter called an antenna unit No. 1 generally designated by the reference numeral 24. Similarly the combination of the antenna element 12 and an electrical conductor extending therefrom to both the phase shifter 18 and the subtraction circuit 20 may be called an antenna unit No. 2 generally designated by the reference numeral 26 and the combination of the antenna element 14 and an electrical conductor extending between the same and the subtraction circuit 22 may be called an antenna unit No. 3 generally designated by the reference numeral 28. The antenna unit 24 is coupled to the antenna unit 26 through the phase shifter and subtractioncircuit '16 and 20 respectively to form a first antenna system generally designated by the reference numeral 30 and the antenna units 26 and 28 are coupled to each other through the phase shifter and subtraction circuit 18 and 22 respectively to form a second antenna system generally designated by the reference numeral 32.

Both the subtraction circuits 20 and 22 are electrically connected to a matrix and data processing circuitry 34, which is well known in the art.

It is now assumed that the antenna elements 10, 12 and 14 are substantially identical in radiation characteristics to each other and that an echo from the particular target (not shown) is incident upon the antenna elements at an angle of of elevation as shown at the arrows in FIG. 1. Under the assumed condition it will be readily understood that as distances between the antenna elements and 12 and between the elements 12 and 14 in the direction parallel to the direction of incident echo are d sin 0 and d sin 0 respectively and that a phase diiference of occurs between signals induced respectively on the elements 12 and 14 where A represents a wavelength for the echo or the transmitted signal from the antenna array. The induced signal from the antenna element 10 passes through the first phase shifter 16 to shift in phase angle by a magnitude of \P1. Similarly the induced signal from the antenna element 12 shifts in phase angle by a magnitude of by means of the second phase shifter 18.

Therefore it will be apparent that a phase diiference I between the outputs from the antenna units 24 and 26 appearing at both inputs to the vectorial subtraction circuit is expressed by the following equation.

Similarly a phase difference I between the outputs from the antenna units 26 and 28 appearing at both inputs to the vectorial subtraction circuit 22 is expressed by the following equation.

sin 0 The subtraction circuits 20 and 22 are operated to vectorially subtract the outputs from the associated antenna units applied thereto from each other. It is here assumed that the output not phase shifted is subtracted from the phase shifted output as shown the plus and minus signs denoted adjacent the inputs to the subtraction circuit.

Since a vectorial diiference between two vectors is maximum in absolute value provided that they are in phase, the values of P are 21ri where i=0, i1, i2 and =21rj where i=0, :1, :2, cause the respective outputs from the subtraction circuits 20 and 22 to be maximum in value. In other Words, when the phase difference I or I has any of the just specified values a radar apparatus including the first or second antenna system 30 or 32 will have a maximum gain. Therefore for any given angle an angle 0 of elevation providing a maximum gain for the first antenna system 30 is expressed by the equation gle 11 an angle 0 of elevation providing a maximum gain for the second antenna system 32 is expressed by the equation where i=0, :1, i2

From the Equation 1 for 0 it is seen that the first antenna system 30 has its gain becoming maximum at a plurality of angles of elevation determined by the values of i. That is, the Equation 1 depicts a multiple-lobed directional pattern of a radar apparatus including the first antenna system 30 with the angular position of the lobe being a function of i. The same is true in the case of the second antenna system 32.

As the angular position of the lobe is a function of the Wavelength divided by the spacing d or d between the adjacent antenna elements, the arrangement of the lobes is different from one to the other antenna system because both antenna systems are different from each other in the Wavelength divided by the distance between the elements and therefore an angular interval between the maximum points on any pair of adjacent lobes. If the phase angles and 0 shifted by the phase shifters 16 and 18 respectively are preselected to cause the maximum point on the mth lobe for the first antenna system 30 to coincide with that on the nth lobe for the second antenna system at an angle 0 of elevation (which may be eX- pressed by 0 =0 =0 then the first and second antenna systems 30 and 32 can be designed and arranged such that the directional pattern of one of both systems includes no lobe coinciding with any lobe included in the directional pattern of the other system at any angle of elevation other than the angle 0 Within an angle of elevation range over which the detection is required to be effected. This results in the definite correspondence between one combination of the shifted phase angles ga and (p and a specified angle 0 of elevation.

The ouputs from both subtraction circuits 20 and 22 or the multiple-lobed directional patterns of the antenna systems 30 and 32 are supplied to the matrix and data processing circuitry 34 where they are combined together to form the coinciding lobe or the main lobe. The patterns are combined in pairs together to cause a selected lobe in one of each pattern pair to coincide with a selected lobe in the other of that pair at a specified angle of elevation with the coinciding lobes different in angle of elevation from one to another combination of patterns. The main lobes thus formed are arranged to cover partly or entirely a space to be searched.

Any one of the antenna elements 10, 12 and 14 may transmit a signal as shown at waveform T in FIG. 2, and all of them receive echoes as shown at waveforms R1, R2 and R3 in the same figure respectively.

- From theforegoing it will be appreciated that the detection apparatus as shown in FIG. 1 is required to include a plurality of antenna systems such as 30 and 32 which increases the scale of the antenna array.

- Referring now to FIG. 3 where in the same reference numerals designate the components corresponding to those shown in FIG. 1, there is illustrated the essential parts of an apparatus constructed in accordance with the teachings of the invention. While FIG. 3 illustrates merely a pair of antenna elements and 12 of the substantially same radiation characteristics disposed in a common vertical planeto be spaced away from each other by a vertical distanceof d only for purpose of illustration it is to be 7 understood that any desired number greater than two of spaced antenna elements may be used.

An antenna element No. 1 designated by the reference numeral 10 is electrically connected to a filter 36 permitting only a predetermined frequency f to pass therethroughand also to another filter 38 permitting only a predetermined frequency f to pass therethrough. The filter 36 is electrically connected through a time delay line 40 to a phase shifter 16 and the filter 38 is electrically con nected to another phase shifter 18. Both phase shifters may be similar to those as previously described in conjunction with FIG. 1. Similarly a second antenna No. 2 iidesignated by the reference numeral 12. is electrically connected to a pair of filters 42 and 44 permitting only the predetermined frequencies f, and f to pass therethrough respectively. The filter 42 is electrically connected to a time delay line 46 which is, in turn, electrically connected to a vectorial subtraction circuit 2.0 to which the phase shifter 16 is also electrically connected. The filter 44 electrically connected to another vectorial subtraction circuit 221to which the phase shifter 18 is also electrically connected. Both the time delay lines 40 and 46 are identical in construction to each other and operative to impart to signals passed therethrough a predetermined common time delay of 1-. The subtraction circuits 20 and 22: may be similar to those as previously described in conjunction with FIG. 1. In other respects, the arrangement is identical to that illustrated in FIG. 1.

Upon transmission any suitable transmitter (not shown) periodically, supplies a radio-frequency energy to one of theantenna elements 10 or 12 in the conventional manner. Then the energized antenna element periodically transmits a signal consisting of a radio-frequency pulse having a frequency of f and a predetermined duration of "r and followed 'by another radio-frequency pulse having a frequency of f different from the frequency 7 and the same duration as the first-mentioned pulse without a spacing therebetween as shown as waveform T in FIG. 4. It is noted that the duration of each pulse is equal to the time. delay provided by each of the time delay lines 40 or 46.

The antenna elements 10 and 12 each receive substantially simultaneously an echo substantially identical to the transmitted signal as shown at waveforms R1 and R'2 in FIG. 4. The waveform R1 received by the antenna element 10 is applied to both the filters 3-6 and 38 to be divided into two waveforms having the respective frequencies of f and f and a common duration of -r. Similarly the waveform R2 is divided into two waveforms having the respective frequencies of f and f and a common duration of 'r by the filters 42 and 44. The waveforms having the frequency of f and corresponding to the transmitted pulse having the same frequency are supplied to the time delay lines 40 and 46 to be given a time delay of 'r. Thus the delayed waveforms will coincide in time with the waveforms having the frequency of f and corresponding to the transmitted pulse having the same frequency. Then all the waveforms are processed in the same manner as previously described in conjunction with FIG. 1. FIG. 4 further shows waveforms R --1, R 1, R -2, R -2 developed at the outputs of the phase shifter 16 the phase shifter 18, the time delay line 46 and the filter 44 respectively.

Therefore it will be readily appreciated that the antenna elements cooperate with each other and with the components 36, 38, 40, 42, 44, 46, 16, 1'8, 20 and 22 to have a pair of multiple-lobed directional patterns each including the maximum lobe points at angles (i or 0 of elevation defined by the equation Sin a2,=(t-% respectively, where M and k represent the wavelengths corresponding to the frequencies of f and f respectively. Assuming that c represents the velocity of electromagnetic wave propagating in the vacuum M=c/f and A =c/f are held. If A A and d are preselected to ho d the relationships then the arrangement of FIG. 3 is identical in directional pattern to that shown in FIG. 1.

The invention has been described as having a pair of time delay lines 40 and 46 connected in the circuit operative with the frequency of 1 thereby to combine the two multiple-lobed directional patterns for each of the frequencies due to the phase difference between the signals induced on the antenna elements together at a common time point. However, it is apparent that the invention is equally applicable to a multiple-beam antenna system in which the time delay lines are omitted and such multiplelobed directional patterns are used as inputs to the associated computer include in the matrix and data processing circuitry 34 in which they are suitably time delayed and combined together at a common time point to form the main lobes at specific angles of elevation respectively.

While the invention has been illustrated and described in terms of a transmitted signal having a pair of different frequencies, it is to be understood that it is equally applicable to a transmitted signal consisting of three or more radio-frequency pulses having different frequencies and a common duration. In this case, an echo received by two antenna elements is divided into a plurality of different frequencies composing the signal through the use of suitable filters. Then for each frequency a multiple-lobed directional pattern is formed in the manner as previously described and the resulting patterns are combined in pairs together to form a plurality of main lobes which in turn cover partly or entirely the space to be searched. For example, with three different frequencies used, the directional patterns of antenna elements are combined together for each of the frequencies such that three lobes, one and only one for each of the patterns corresponding to each of the frequencies, coincide at predetermined angle of elevation.

Alternatively three or more antenna elements may cooperate with a plurality of different frequencies composing a transmitted signal with the satisfactory results. Also this measure may be advantageously applied to a combination of an antenna array including a plurality of antenna elements disposed at different intervals in a common vertical plane and operative with a plurality of different frequencies.

From the foregoing it will be appreciated that the objects of the invention have been accomplished by the provision of a radio detection apparatus comprising at least two antenna elements having the substantially same radiation characteristics and disposed at a predetermined interval greater than one half an operating wavelength, one of the antenna element being arranged to transmit periodically radio-frequency pulses, each of Which consists of a plurality of continuous radio-frequency pulses having different frequencies and a common duration and successively arranged with respect to time to form no spacing therebetween, fiter means for dividing an echo received by all the antenna elements into the plurality of radio-frequency pulses having the different frequencies, and means for forming a multiple-lobed directional pattern for each of the different frequencies.

While the invention has been illustrated and described in conjunction with several preferred embodiments thereof it is to be understood that various changes in the details of construction and the arrangement and combination of parts may be resorted to Without departing from the spirit and scope of the invention.

What is claimed is:

1. In a radio detection apparatus: the combination of an antenna array including at least two antenna elements of substantially the same radiation characteristics disposed in a common vertical plane and spaced from each other by a predetermined interval greater than one half an operating wavelength; one of said antenna elements serving to periodically transmit radio-frequency pulses having different frequencies and a common duration and successively arranged with respect to time to form no spacing therebetween; filter means for dividing the echo received by all of said antenna elements into radio-frequency pulses each of which has one frequency and common duration; means for processing the divided pulses of the same frequency to form a multiple-lobed directional pattern of said antenna array for each of said different frequencies, and data processing means for combining a plurality of said multiple-lobed directional patterns in pair together.

2. A radio-detection apparatus as claimed in claim 1 wherein said data processing means combine said multiplelobed directional patterns in pairs together such that a selected lobe in one of each of the combined pattern pairs coincides with a selected lobe in the other of that pair at an angle of elevation to form a plurality of the main lobes difierent in angle of the elevation from one to another combination of the pattern pair with said main lobes covering at least one portion of a space to be searched.

3. A radio detection apparatus as claimed in claim 1 wherein time delay circuit means for imparting different time delays to the said respective divided pulses to permit the pulses to be processed at a common time point and operational means for vectorially subtracting the said divided pulse for each of said different frequencies to form said multiple-lobed directional pattern, and said data processing means combine said multiple-lobed directional patterns in pairs together such that a selected lobe in one of each of the combined pattern pairs coincides with a selected lobe in the other of that pair at an angle of elevation to form a plurality of the main lobes different in angle of elevation from one to another combination of the pattern pair with said main lobes covering at least one portion of a space to be searched.-

4. A radio detection apparatus as claimed in claim 1 wherein said pulse processing means include operational means for vectorially subtracting the said divided pulses for each of said different frequencies to form said multiple-lobed directional pattern, said data processing means cause said pulses to be processed at a common time point, thereby combining the directional patterns in pairs together such that a selected lobe in one of each of the combined pattern pairs coincides with a selected lobe in the other of that pair at an angle of elevation to form a plurality of the main lobes different in angle of elevation from one to another combination of the pattern pair with said main lobes covering at least one portion of a space to be searched.

5. In a radio detection apparatus: an antenna array including at least two antennas; each antenna having substantially the same radiation characteristics and spaced apart from one another a distance greater than one half of a predetermined operating wavelength; one of said antenna being capable of periodically transmitting radiofrequency pulses, each pulse itself comprising a plurality of radio-frequency pulses having different frequencies and a common duration and successively arranged with respect to time whereby no spacing exists therebetween; and means for dividing each echo pulse received by all said antennas into a plurality of return radio-frequency pulses each having a frequency'similar to one of said different frequencies and all having a duration similar to said common duration.

6. In a radio detection apparatus according to claim 5; further including time delay means for imparting different time delays to the divided return radio-frequency pulses to coordinate all said return pulses at a common point in time.

7. In a radio detection apparatus according to claim 6; further including means for vectorially subtracting the divided return pulses of a similar frequency received from different antennas.

References Cited UNITED STATES PATENTS 12/1966 Renn et al. 3/ 1967 Tamama.

US. Cl. X.R. 343-100, 113

UNITED STATES PATENT OFFICE CERTIFICATE OF CORRECTION Patent No. 3 s 510 s 871 Dated May 5 I 1970 Inventor(s) Maseru WATANABE et a1 It is certified that error appears in the above-identified patent and that said Letters Patent are hereby corrected as shown below:

Col. 1, line 2 4, delete "shift" insert --shi;fted--;

C01. 3, lin 60, delete b =ll) i insert l 77* 25% sin e'- line 67, delete t g sin 9" insert 21rd 2 $2 sin 6--; Col. l line 16, delete (1 E insert A 1 2n (i 1 d1 2? line 25, delete 11E)" insert 2 2' A IP2) E? line 45, delete P and insert 111 and lP line 58, delete f insert gb line 59 delete insert 111 Col. 5, line 50, delete "f (second occurrence) insert --f Col. 6, line 10, delete "(1 11% n insert t1 g line l t, delete "(i 5.) insert j i2) line 36, delete "include" insert --included--; Signed and sealed this 22nd day of December 1970.

Amen

M mmhu' mum is. Attcstmg Officer oomissioner of Patents- FORM PC4050 meal USCOMM-DC ooa7e-poq U S GOVRNMENT PRINTING OFFICE: l9, O36"'!!l 

